2005. King, Philip B., Arndt, Raymond E., Schruben, Paul G., Bawiec, Walter J., and Beikman, Helen M. This line shapefile shows the outlines of geologic units within the United States. This layer is part of the Geologic Map of the United States, ori... Geological Survey (U.S.).

1994. King, Philip B., Arndt, Raymond E., Schruben, Paul G., Bawiec, Walter J., and Beikman, Helen M. This polygon shapefile shows the boundaries of geologic units within the United States. This layer is part of the Geologic Map of the United States... Geological Survey (U.S.).